1. Field of the Invention
The present invention relates to an optotype presenting apparatus which presents an optotype such as an optotype for a visual acuity test and an optotype for a binocular vision test.
2. Description of Related Art
Conventionally, there is known an optotype presenting apparatus of a display type such that various optotypes are displayed on a screen of a display unit (see Japanese Patent Application Unexamined Publication No. 2006-42978). In this optotype presenting apparatus, when presenting binocular optotypes for a binocular vision test to an examinee, a technique for displaying a three-dimensional image can be used in order to present different optotypes to a right eye and a left eye of the examinee (see Japanese Patent Application Unexamined Publication No. 2002-311385, and U.S. Pat. No. 5,638,082 corresponding to Japanese Patent Application Unexamined Publication No. Hei 07-322304).
FIG. 6 is a longitudinal sectional view of a color liquid crystal display unit 30 and a polarization optical member 50 placed in front of the display unit 30 in an optotype presenting apparatus which uses the same technique for displaying a three-dimensional image as that of Japanese Patent Application Unexamined Publication No. 2002-311385. In front of a liquid crystal 31 of the display unit 30, an oriented film 32b, a transparent electrode 33b, a color filter 40 in which R, G and B filters are arranged in each of pixels 42, a transparent supporting member 34b, and a polarizing plate 35b are placed in order. The polarization optical member 50 is placed in front of the polarizing plate 35b and comprises optical regions 55a and 55b which are in the form of a lateral line (laterally long) corresponding to the arrangement of the pixels 42 in a lateral direction (a horizontal direction), and are alternately arranged in a longitudinal direction (a vertical direction). Light from the display unit 30 is converted by the optical regions 55a and 55b so that light passing through the optical regions 55a and light passing through the optical regions 55b have polarizing axes perpendicular to each other. By placing a polarizing filter which has a polarizing axis coinciding with the polarizing axis of the light passing through the optical regions 55a in front of either one of the examinee's right and left eyes, and placing a polarizing filter which has a polarizing axis coinciding with the polarizing axis of the light passing through the optical regions 55b in front of the other eye, different optotypes are presented to the right eye and the left eye, whereby a binocular vision test can be performed.
Light in a direction of the normal P01 via the pixels 42 is converted by the optical regions 55a and 55b so that light passing through the optical regions 55a and light passing through the optical regions 55b have polarizing axes perpendicular to each other. Here, the light via the pixels 42 heads also for a direction P02 other than the direction of the normal P01 and passes as leakage light through the optical regions 55a and 55b alternately arranged adjacent to each other in the longitudinal direction, because there is a gap having a thickness of the supporting member 34b (about 1 mm) between the pixels 42 and the polarization optical member 50. When the examinee looks the display unit 30 on which the binocular optotype is displayed, substantially from the direction of the normal 201, the leakage light hardly reaches the eye, so that the test can be performed with accuracy. However, when the examinee cannot see the display unit 30 on which the binocular optotype is displayed from the direction of the normal P01, the test cannot be performed with accuracy because the leakage light tends to reach the eye.